The present invention relates generally to systems for dispensing cryogenic fluids from vessels storing cryogenic liquids and, more particularly, to a dispensing system for cryogenic liquid bulk vessels that provides cryogenic fluids at high pressures and high flow rates.
Cryogenic gases are used in a variety of industrial and medical applications. Many of these applications require that the cryogen be supplied as a high pressure gas. For example, high pressure nitrogen and argon gases are required for laser welding while high pressure nitrogen, oxygen and argon gases are required for laser cutting. Gas pressure and flow rate requirements for industrial lasers in the range of approximately 400-420 psig and approximately 1500-2500 scfh, respectively, are now typical. Cryogens such as nitrogen, argon and oxygen are typically stored as liquids in vessels, however, because one volume of liquid produces many volumes of gas (600-900 volumes of gas per one volume of liquid) when the liquid is permitted to vaporize/boil and warm to ambient temperature. To store an equivalent amount of gas requires that the gas be stored at very high pressure. This would require heavier and larger tanks and expensive pumps or compressors.
Advances in industrial laser technologies have increased the flow requirements for cutting assist gases that exceed the capability of prior art cryogenic storage vessels and their associated pressure building systems. Specifically, the pressure building capabilities of prior art systems limit the flow of pressurized gas available for such applications.
Prior art vessel pressure building systems were designed with the philosophy that pressure building gas delivered to the head space of a vessel should be at the same temperature as the liquid cryogen in the vessel so as to avoid undesirable warming of the liquid cryogen. As such, prior art pressure building systems typically simply change the state of liquid cryogen from the vessel to vapor and direct the vapor to the head space of the vessel without adding any additional heat beyond that required for vaporization. In addition, traditional fluid flow thought would suggest that the pressure building process would be impaired if the flow were directed through traps in the flow path.
Experiments have shown, however, that a significant stratification of the inner vessel vapor or head space exists when warmed gas or vapor is introduced thereto. In addition, experiments have shown that further expanding the pressure building gas or vapor by adding more heat prior to delivering it to the head space of the vessel significantly increases the pressure building performance of the system. Prior art systems have failed to take advantage of these discoveries.
Accordingly, it is an object of the present invention to provide a high flow pressurized cryogenic fluid dispensing system that builds pressure very rapidly.
It is another object of the present invention to provide a high flow pressurized cryogenic fluid dispensing system that maintains pressure during dispensing at a variety of liquid temperatures.
It is another object of the present invention to provide a high flow pressurized cryogenic fluid dispensing system that provides a flow rating that is sufficient to supply cryogenic gas to multiple lasers.
It is another object of the present invention to provide a high flow pressurized cryogenic fluid dispensing system with pressure building that cycles on and off so that the heating/pressure building coils of the system at least partially thaw between cycles.
It is still another object of the present invention to provide a high flow pressurized cryogenic fluid dispensing system that reduces or eliminates safety vent losses.
It is still another object of the present invention to provide a high flow pressurized cryogenic fluid dispensing system that is economical to construct and maintain and that is durable.
Other objects and advantages will be apparent from the remaining portion of this specification.
The present invention is directed to a system for dispensing pressurized cryogenic fluids at high flow rates. The system of the present invention features a pressure building capability that is improved over the prior art, and thus offers a higher maximum flow capability. The system features a pressure building coil that includes a section of parallel heat exchangers and a section of series heat exchangers that are in communication with one another. An automatic pressure building regulator valve, when opened, permits cryogenic liquid from the system tank to enter the pressure building coil. Liquid entering the section of parallel heat exchangers flashes so that gas is produced. Surge check valves direct the gas into the section of series heat exchangers where it is warmed and pressurized. The warmed and pressurized gas is directed to the head space of the tank through a pair of flapper check valves so that the tank is rapidly pressurized. A controller opens the pressure building regulator valve and closes the vapor space withdrawal control valve when the pressure within the tank drops below the operating pressure/set point of the system.
Due to the improved pressure building, the gas use circuit of the system, which leads from the head space of the tank or the outlet of the pressure building coil through a warming coil to the use device or point, simply warms gas instead of vaporizing liquid from the tank. This reduces the number and size of heat exchangers required in the gas use circuit.
The system may optionally be constructed with a turbo circuit featuring a turbo line leading from the parallel section header to a venturi mixer positioned in the gas/vapor line leading to the warming coil. A turbo control valve is positioned in the turbo line. When the turbo valve is open, liquid from the parallel section header is injected into the gas flowing to the warming coil and is vaporized so that a greater gas flow rate is provided by the system. The turbo circuit therefore increases the flow rate capability of the system without additional heat exchangers. The turbo circuit thus increases the flexibility of the system.
The system may also be equipped with a rattle valve that receives exhausted pressurized air from the automatic valve control system. The rattle valve is positioned upon the section of parallel heat exchangers and vibrates so that ice is removed therefrom.
The following detailed description of embodiments of the invention, taken in conjunction with the accompanying drawings, provide a more complete understanding of the nature and scope of the invention.